Re: [dpdk-users] Dpdk poor performance on virtual machine

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 15 Dec 2016 14:33:25 +0000
"Hu, Xuekun" <xuekun.hu@intel.com> wrote:

> Are you sure the anonhugepages size was equal to the total VM's memory size? 
> Sometimes, transparent huge page mechanism doesn't grantee the app is using
> the real huge pages. 
>  
> 
> -----Original Message-----
> From: users [mailto:users-bounces@dpdk.org] On Behalf Of edgar helmut
> Sent: Thursday, December 15, 2016 9:32 PM
> To: Wiles, Keith
> Cc: users@dpdk.org
> Subject: Re: [dpdk-users] Dpdk poor performance on virtual machine
> 
> I have one single socket which is Intel(R) Xeon(R) CPU E5-2640 v4 @ 2.40GHz.
> 
> I just made two more steps:
> 1. setting iommu=pt for better usage of the igb_uio
> 2. using taskset and isolcpu so now it looks like the relevant dpdk cores
> use dedicated cores.
> 
> It improved the performance though I still see significant difference
> between the vm and the host which I can't fully explain.
> 
> any further idea?
> 
> Regards,
> Edgar
> 
> 
> On Thu, Dec 15, 2016 at 2:54 PM, Wiles, Keith <keith.wiles@intel.com> wrote:
> 
> >  
> > > On Dec 15, 2016, at 1:20 AM, edgar helmut <helmut.edgar100@gmail.com>  
> > wrote:  
> > >
> > > Hi.
> > > Some help is needed to understand performance issue on virtual machine.
> > >
> > > Running testpmd over the host functions well (testpmd forwards 10g  
> > between  
> > > two 82599 ports).
> > > However same application running on a virtual machine over same host
> > > results with huge degradation in performance.
> > > The testpmd then is not even able to read 100mbps from nic without drops,
> > > and from a profile i made it looks like a dpdk application runs more than
> > > 10 times slower than over host…  
> >
> > Not sure I understand the overall setup, but did you make sure the NIC/PCI
> > bus is on the same socket as the VM. If you have multiple sockets on your
> > platform. If you have to access the NIC across the QPI it could explain
> > some of the performance drop. Not sure that much drop is this problem.
> >  
> > >
> > > Setup is ubuntu 16.04 for host and ubuntu 14.04 for guest.
> > > Qemu is 2.3.0 (though I tried with a newer as well).
> > > NICs are connected to guest using pci passthrough, and guest's cpu is set
> > > as passthrough (same as host).
> > > On guest start the host allocates transparent hugepages (AnonHugePages)  
> > so  
> > > i assume the guest memory is backed with real hugepages on the host.
> > > I tried binding with igb_uio and with uio_pci_generic but both results  
> > with  
> > > same performance.
> > >
> > > Due to the performance difference i guess i miss something.
> > >
> > > Please advise what may i miss here?
> > > Is this a native penalty of qemu??
> > >
> > > Thanks
> > > Edgar  
> >
> > Regards,
> > Keith
> >
> >  

Also make sure you run host with 1G hugepages and run guest in hugepage
memory. If not, the IOMMU has to do 4K operations and thrashes.